In a plasma processing apparatus, a substrate to be processed (“substrate”) is carried into a chamber, and a predetermined processing gas is supplied into the chamber. Then, plasma of the processing gas is generated within the chamber. A predetermined processing such as, for example, etching or film forming is performed on the substrate by the generated plasma of the processing gas. In the plasma processing, for example, a pressure within the chamber or a flow velocity of the processing gas supplied into the chamber is one of important factors that influence the properties of the processed substrate. Also, when a deviation occurs in a distribution of a pressure within the chamber or a flow velocity of the processing gas, non-uniformity of a property such as, for example, a critical dimension (CD) is increased within the plane of the substrate. Therefore, it is desirable that the distribution of the pressure within the chamber or the flow velocity of the processing gas is uniform within the plane of the substrate.
Since the supply of the processing gas may be performed above the center of the substrate, the processing gas may be substantially uniformly supplied over the entire circumference of the substrate. However, in the exhaust of the processing gas, it is difficult to dispose an exhaust device below the center of the substrate due to the structure of a plasma processing apparatus. Thus, the exhaust device is provided at a position spaced away from the top of the central axis of the substrate. Thus, in the circumferential direction of the substrate, a distance to the exhaust device is varied, and an exhaust amount of the processing gas on the substrate is varied depending on the distance to the exhaust device. This causes a deviation in a distribution of a pressure or a flow velocity of the processing gas on the substrate.
In order to avoid this, it is considered, in a baffle plate provided between a processing space in which plasma is generated and an exhaust path that exhausts the processing gas and having a plurality of through holes, to decrease an opening area of a through hole closer to the exhaust device and increase an opening area of a through hole farther from the exhaust device. Accordingly, in the circumferential direction of the substrate, an exhaust conductance becomes lower at a position closer to the exhaust device, and becomes higher at a position farther from the exhaust device. Accordingly, the exhaust amount of the processing gas on the substrate becomes more uniform in the circumferential direction of the substrate, thereby suppressing the deviation in the distribution of a pressure or a flow velocity of the processing gas on the substrate. See, e.g., Japanese Utility Model Laid-Open Publication No. 5-4466.